This application is a continuation of U.S. patent application Ser. No. 865,869, filed May 22, 1986.
The present invention relates to the art of gas separation. It finds particular application in the separation of substantially pure oxygen gas from atmospheric air and will be described with particular reference thereto. However, it is to be appreciated that the present invention is applicable to the purification of oxygen from other sources and to the separation or purification of other gases.
Heretofore, oxygen has commonly been separated from atmospheric air by selective adsorption. Atmospheric air was cyclically pumped into one of a pair of beds filled with a physical separation material. The physical separation material, such as 5A Zeolite, permitted the less strongly adsorbed molecules such as oxygen and argon, to pass therethrough but trapped or retained the more strongly adsorbed molecules of nitrogen, carbon dioxide, and water vapor. When the trapping or adsorption capacity of the bed was substantially met, the air was pumped to the second bed while the first bed was evacuated or cleansed of the nitrogen and other molecules.
By carefully controlling the cycling of gas between the beds and other operating parameters, about 95% pure oxygen could be generated at the output to the beds. However, if too much flow is passed through the system during a cycle, the adsorption capacity of the beds will be exceeded and the purity of the product oxygen will become substantially less than the maximum purity limit of 95.7% or the normal 95% output of typical concentrators.
Oxygen composes about 20% of atmospheric air whereas argon composes about 1%. When nitrogen, carbon dioxide, and other larger molecules are removed from atmospheric air leaving substantially only oxygen and argon, the percentages of argon and oxygen in the separated gas increase about five fold. That is, even if the separator works perfectly, passing only oxygen and argon, the resultant product gas will be 4% to 5% argon and 95% to 96% oxygen. Thus, the purity of the resultant oxygen gas is limited by the argon content of atmospheric air. That is, the roughly 1% concentration of argon in the atmospheric air limits the purity of the separated oxygen to a maximum possible purity of about 95% or 96%.
In accordance with the present invention, a method and apparatus are provided for reducing the argon contamination of the separated oxygen and raise its purity.